absorb Pyflex as a core module of Pyatoa

[bch0w]

Pyflex is a relatively small package, with most of the algorithm contained in the window_selector.py script.
It may be useful to absorb Pyflex into Pyatoa so that we can coalesce documentation, have one less repository to deal with, and simplify install procedure and future maintenance and development.

This will simplify development of future windowing capabilities because we won't need to update an entire other repository to make a change, which would involve updating dependencies, bumping version numbers etc. In the process we can clean up the Pyflex source code since it hasn't been looked at in a while.

I envision the change would go:

1. pyflex.window_selector -> pyatoa.core.windower
2. pyflex.config -> pyatoa.core.config (absorb)
3. pyflex.interval_scheduling/stalta/utils -> pyatoa.core.utils.window

We can stick a message on the Pyflex repo that future development will happen in Pyatoa.
Also ensure that proper contributions are cited.

[bch0w]

This is likely more work than it's worth. but something to keep in mind